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mod for MXL v57m ??
Old 20th January 2007
  #1
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mod for MXL v57m ??

I was wondering if anyone knew of a mod for the MXL V57M ldc mic... i have one and it sounds ok, but i think i had heard of some mods for it in the past..

just wondering if anyone knew of any or had any links to some..

thx
Old 20th January 2007
  #2
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Hmmm.... Do you have schematics or a photo of what is inside curently?
Old 20th January 2007
  #3
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heres some photos..

i can give you specifics if you need some

thx
Attached Thumbnails
mod for MXL v57m ??-mxl_v57m_1701.jpg   mod for MXL v57m ??-mxl_v57m_1702.jpg  
Old 20th January 2007
  #4
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The first pic shows a voltage convertor to bring voltage back to +48 to polarize the capsule, the second one shows a FET with spilt load and couple of emitter followers that are responsible for harsh sound on highs.

I recently modified my pair of 707'th using couple of good mic transformers 150 Ohm : 15K

If you have some that can fit inside of your mic I can help you with schematics.
Old 21st January 2007
  #5
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what would you identify as the FETs in the second picture?
Old 21st January 2007
  #6
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Quote:
Originally Posted by lpkyer View Post
what would you identify as the FETs in the second picture?
A black pimple that sits on top of the picture between 1G resistors.
Old 21st January 2007
  #7
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Quote:
Originally Posted by Wavebourn View Post
A black pimple that sits on top of the picture between 1G resistors.
thanks Time for modding my second mxl 2001...
Old 21st January 2007
  #8
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it is only identified as

K170
GRDF

thx for all the help
Old 21st January 2007
  #9
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It is calles 2SK170
Last name is Toshiba


Quote:
Originally Posted by Disjointed View Post
it is only identified as

K170
GRDF

thx for all the help
Old 21st January 2007
  #10
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Mine had everything on the single PCB:
http://wavebourn.com/images/audio/mxl04.gif

How it looks after modification:

http://wavebourn.com/images/audio/mxl09.gif

I'm waiting for samples of mic trannies from one supplier, going to try them as well.
Old 22nd January 2007
  #11
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i wish you would have had 2 pics of the same view of your mod...
i could only tell what looks like a new cap (white).. and a big can of something...

so is there a simple way to mod my mic... im good with electrical work, but not so good with calculations and such yet...??

change some caps?
change the fet?

????
Old 22nd January 2007
  #12
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It is the another case when different design gives more improvements than usage of golden-platinum-whatever parts in the current one.

That metal can on the picture is the microphone transformer that helps to achieve low dynamic output impedance between wires consuming low phantom powering current through them.

Edit: today I've got samples of Amtran C-3402-2 transformers, gonna try them...
Old 23rd January 2007
  #13
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so basically what youre saying is theres no simple 'golden' mod... but it would need a great re-design of internal components to make it sound better..

??
Old 23rd January 2007
  #14
Quote:
Originally Posted by Disjointed View Post
i wish you would have had 2 pics of the same view of your mod...
i could only tell what looks like a new cap (white).. and a big can of something...

so is there a simple way to mod my mic... im good with electrical work, but not so good with calculations and such yet...??

change some caps?
change the fet?

????
Try the Siliconix J305 for the fet. It's a very low stray capacitance low noise fet with great RF bandwidth. I find it has better details and is more open than the 2sk170. Re-bias may be required.

Jim Williams
Audio Upgrades
Old 24th January 2007
  #15
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Quote:
Originally Posted by Disjointed View Post
so basically what youre saying is theres no simple 'golden' mod... but it would need a great re-design of internal components to make it sound better..

??
Some people even don't believe that such "great" may give improvement unless you replace the entire capsule with something that has shifted high freq resonances to twice higher frequencies... They believe that the entire boost around 9 KHz is bad; I believe that distortions on high end of spectrum are worse, and they are the result of attempt to achieve low output resistance consuming low current through exactly the same wires without any transformation.
Old 24th January 2007
  #16
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Actually, your MXL V57 had "the mods" done at the factory.
A couple of years ago, Scott Dorsey wrote an article about modifying the V67 to remove the horrible transformer in it, and replace the circuitry with a transformerless circuit he called "The Schoeps Circuit" because he first saw it in a Schoeps microphone. Before he published the article in Recording magazine, he had some contact with Marshall (MXL) and suggested they could provide the public with better microphones while reducing their costs by eliminating that cheap, low-quality transformer and replacing it with a simple circuit. When the article finally came out, I went to MARS to buy a couple of Shanghai mikes on which to perform the mods. There are dozens of different brands and models of these mikes, and they're mostly identical, all coming from the same factory in Shanghai. Since I was going to gut mine, I sought out the cheapest ones I could find, which turned out to be the brand new V57m. I opened them up in the store and saw that they actually already have a circuit very similar to Scott's "Schoeps" circuit. About the only real difference was the addition of a DC-DC converter board which produces a higher capsule polarizing voltage. This increases headroom in the front end of the microphone, but may exacerbate some other capsule deficiencies involving frequency response or noise. But the improvement over the V67 was huge, owing primarily to the crummy transformer that was in there.
Other than Wavebourn here, nobody's really complaining about the sound of this circuit. Yes, you could work backwards and install an output transformer, but you'd have to spend a fair amount of money on a good transformer in order to come out ahead. Most mods to the V57 involve simple component upgrades, which I think are more cost-effective than a transformer. The 2SK170 is the FET most people upgrade TO, so if it's already in there then I would leave it alone. I actually never did any mods to my V57s because they were already cleaned up enough that it hasn't been a priority - I wouldn't expect the changes to be dramatic enough to make it a fun project. Of course, I never ever USE these mikes because they still don't sound as good as some other mikes I've got (most of which use transformers) so there you go. I think it has more to do with the capsule and grill than the electronics - that circuit is used on some very highly-regarded microphones.

If you do want to fiddle with that microphone, start by replacing those two electrolytic coupling caps with metallized polyester film caps. Then have a look at those two output transistors and see if there's something better that could be used. The specific components in these mikes seems to vary from day to day, so they could be anything. I probably wouldn't mess with the DC-DC board. Any work you do needs to be done very carefully, and the board needs to be defluxed when you're done (without messing up the capsule, of course!)
Old 24th January 2007
  #17
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Quote:
Originally Posted by ulysses View Post
Actually, your MXL V57 had "the mods" done at the factory.
...to replace cheap transformer by cheaper transistors. Now, if to replace a capsule by electret button it will be even cheaper.
Old 25th January 2007
  #18
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I think one of the points of the v67 is that it had a transformer and it would produce a different sound than their other typically hyped mics. A worse problem in it is that many of the v67's are poorly biased. It was killing the headroom in mine.
Old 25th January 2007
  #19
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thanks for the replies...

i really like the background info ulysses..

how would i go about checking the bias / re-biasing.. (replacing a resistor right?)
Old 25th January 2007
  #20
Marshall didn't get the idea of the Schoeps stye circuit from Scott, they got it from Rode. I designed a similar circuit for the NT-2 back in 1995. It's been around for a while now. I like to use MIT coupling caps and a .001 uf off the capsule bypassed with a Wima 100 pf 1kv film and foil polyprop cap. A Cornel Dublier silver mica also has a nice sound.

Forget Jap fets, I go with a Siliconix J305, a very fast, low capacitance low noise fet with fantastic transient reponse. The 2SK's sound filtered to me. Low level details are masked with those fets. Swap them and you will understand.

I use Hitachi output transistors with great linearity and .5 nv/hz/sq noise. Messing with the bias oscillator is always a good idea. Most of these Asian mics use the similar Schoeps style oscillator to increase bias over 48 volts to achieve good capsule sensitivity. Unfortunately, most hover around 40 volts after all is done so capsule sensitivity is compromised. I found some transistors in these circuits don't have the power bandwidth to deliver the necessary AC swing to be rectified into a usable polarization voltage. Some have it but the 1N4148 diodes don't have the current availability to reach above 40 volts even with voltage multipliers.

The solution is to use a decent transistor with very fast, 1 amp rectifier diodes. I've been able to raise polarization voltages from 40 to 57 volts by the swap of these components. Mic sensitivity increases around 6 db while the use of the lower noise parts also lowers amplifier noise for a net gain in S/N ratio. These modified mics are very quiet and sound very good.

BTW, that Schoeps emitter output design is sensitive to loading. The worst distortion will be found driving the primary of a mic pre input transformer. For those apps, a small series output resistor around 22 ohms can help as the load is not only the AC impedance, but the relativly low DC resistance. Driving active mic preamps with a 4k or higher input impedance offers the best linearity for that design.

Jim Williams
Audio Upgrades
Old 25th January 2007
  #21
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Quote:
Originally Posted by Jim Williams View Post
Most of these Asian mics use the similar Schoeps style oscillator to increase bias over 48 volts to achieve good capsule sensitivity.
No. They have to bias emitter followers hardly loading weak phantom power, so need to bring the voltage back using high frequency oscillator with doubling rectifier. This high frequency soaks into a signal path causing rectification on base - emitter junctions loaded by capacitors worseing the result. However, original design used chokes to minimize this effect, MXL manufacturers use low ohm resistors instead.

Quote:
Unfortunately, most hover around 40 volts after all is done so capsule sensitivity is compromised.
Unfortunately, it is impossible to get 150 Ohm output impedance with 6.81K resistors in emitters with low enough distortions so they have to load phantom power hardly. It causes voltage drop on 6.8K resistors (in my mics the resulting phantom power was 32V) that is too small to power the capsule.

Quote:
I found some transistors in these circuits don't have the power bandwidth to deliver the necessary AC swing to be rectified into a usable polarization voltage. Some have it but the 1N4148 diodes don't have the current availability to reach above 40 volts even with voltage multipliers.
You can't get more than twice of voltage powering this oscillator after rectifying it's output by voltage doubling rectifier, no matter what diodes and transistors you use. Also, please keep in mind that the entire oscillator dissipates power causing more voltage drop that it is used to compensate...

Quote:

BTW, that Schoeps emitter output design is sensitive to loading. The worst distortion will be found driving the primary of a mic pre input transformer.
No.
The primary of inpit transformer is not a problem, it could be a problem on the lower end in case of too low inductivity of mic transformers. I did not see consoles, even cheapest ones, that have so low inductivity that may cause any problems for microphones with 150 Ohm output impedance.

The worst case in the particular case is is to drive capacitive load. That emitter followers are made to drive capacity of cables. But it is not the whole story. They have internal capacitors from emitters to ground to prevent soaking of high frequency from voltage convertor to input of microphone amplifier. Base - emitter junctions rectify both soaked into signal path high frequency from voltage converter and high end of spectrum of the signal distorting it.

Quote:
For those apps, a small series output resistor around 22 ohms can help as the load is not only the AC impedance, but the relativly low DC resistance. Driving active mic preamps with a 4k or higher input impedance offers the best linearity for that design.
They have already 22 Ohm resistors in series with each emitter, and already have capacitors after them. That emitter followers and internal capacitors even without capacitances of cables cause harsh sound on high end of spectrum that is called "Chinese Sound". Actually, the envelope of rectified highs intermodulate with lows causing specific "coloration". No matter how high is input impedance of mic amp harsh highs are guarranteed.

What I did with my microphones, I made class A very linear amplifier using one FET and one BJT from the original microphone. Transistors are very good for the mic, though were improperly used. The amp is loaded by 2.7 K resistor, has deep feedback by voltage, so have very low output resistance, but is powered through high resistances from phantom power, so to minimize distortions and achieve symmetrical output I used a good microphone transformer. Load of phantom power by my amp is very light comparing to the original, so I did not need to compensate the voltage drop using high frequency oscillator that causes additional troubles.


Believe, that "Chinese Sound", or sometimes called "Broken Glass" coloration disapeared, despite some people believe that it is the result of cheap capsule. No, it is the result of cheap electronics that turned good professional prototype of the chinese microphone into a chinese toy.
Old 25th January 2007
  #22
[QUOTE=Wavebourn;1092143]No. They have to bias emitter followers hardly loading weak phantom power, so need to bring the voltage back using high frequency oscillator with doubling rectifier. This high frequency soaks into a signal path causing rectification on base - emitter junctions loaded by capacitors worseing the result. However, original design used chokes to minimize this effect, MXL manufacturers use low ohm resistors instead.

That only filters the oscillator leakage out of the output cables, it does nothing for the leakage into the audio preamps in the mic body. Check out a U-87AI, 414B, 451 or any number of respected mics and you will see oscillator leakage all over the preamp. I view this as no more serious than 200k record bias on magnetic tape, which by it's nature is much higher in relative amplitude than oscillator leakage in a mic.

Unfortunately, it is impossible to get 150 Ohm output impedance with 6.81K resistors in emitters with low enough distortions so they have to load phantom power hardly. It causes voltage drop on 6.8K resistors (in my mics the resulting phantom power was 32V) that is too small to power the capsule.

The zeners set those voltage levels, I get around 36 volts typical, works fine.

You can't get more than twice of voltage powering oscillator after rectifying it's output by voltage doubling rectifier, no matter what diodes and transistors you use.

However, losses in the rectification can lower them substantially. This is how a 20v pk tp pk waveform won't reach above 42 volts with a 2 stage multiplier.

No.
The primary of inpit transformer is not a problem, it could be a problem on the lower end in case of too low inductivity of mic transformers. I did not see consoles, even cheapest ones, that have so low inductivity that may cause any problems for microphones with 150 Ohm output impedance.

The worst case in the particular case is is to drive capacitive load. That emitter followers are made to drive capacity of cables. But it is not the whole story. They have internal capacitors from emitters to ground to prevent soaking of high frequency from voltage convertor to input of microphone amplifier. Base - emitter junctions rectify both soaked into signal path high frequency from voltage converter and high end of spectrum of the signal distorting it.

Well, breadboard up the circuit, feed it into an Audio Precision and load it to 1200 ohms. Do a distortion vs amplitude test. Now, load it with 4k and sweep over the previous test. See the difference?

They have already 22 Ohm resistors in series with each emitter, and already have capacitors after them. That emitter followers and internal capacitors even without capacitances of cables cause harsh sound on high end of spectrum that is called "Chinese Sound". Actually, the envelope of rectified highs intermodulate with lows causing specific "coloration". No matter how high is input impedance of mic amp harsh highs are guarranteed.

If anything, this would be called, "the Schoeps sound", many seem to like it. The Chi-com sound is the result of using capsules with severe resonance in the higher frequencies offering the glass breaking 10k boost of 5 to 9 db typical. If I ever need 9 db at 10k, I must certainly have hearing damage.


Jim Williams
Audio Upgrades
Old 25th January 2007
  #23
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Quote:
Originally Posted by Jim Williams View Post
The Chi-com sound is the result of using capsules with severe resonance in the higher frequencies offering the glass breaking 10k boost of 5 to 9 db typical. If I ever need 9 db at 10k, I must certainly have hearing damage.
Jim;

it is the myth.
Reality is, the capsule has to be infinite thin to have no resonances on highs (if you go higher you will see a comb).
The originals were used for AM broadcast recordings where flat up to 20 KHz response was not necessary, thick capsules with 9K resonance were much cheaper than twice thinner capsules with 20K resonances, but they worked well without the "Chinese Coloration" (Call it Shoeps sound that many love, don't matter).
This single peak can be easily equalized by a channel strip EQ. But that "Chinese Coloration" can't. The only way is to replace internal electronics, and it was exactly what I did.
Initially, I wanted to put the EQ inside of the mic, I've calculated already all needed values, but gave up the idea after listening to it modified. I already have an EQ in channel strips, and I switch them on for other purposes than equalizing 9K boost, so anyway if it is on so I use it.
However, I can modify mics for somebody who wants, including the EQ inside, so the frequency response will be flatter.
Old 26th October 2007
  #24
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Mods to MXL V57m (MXL990)

The balancing of the impedance of both output XLRpins 2 and 3 can be improoved. This improoves the insensitivity of the mike cable for picking up static and magnetic noises and 50Hz mains hum. Impedances of XLR pins 2 and 3 compared with each other should be within 1 % over the frequency range of at least 50Hz up to 50 kHz !! If this is true, all noises on de signal wires will be attenuated by 40dB due to the balancing action of the microphone amplifier stage in the mixer console input. Noise suppression is only as good as the impedance balance of the soundsource is !!!
-----
1) Replace C1 and C2 by condensers of the same type and value, but within 1% value to each other. (NB: they only need to be equal within 1%). This balances out high frequency noise (mains switches / FL lamps etc).
2) Replace r1 and r2 (were only 20 ohms) by 180 ohms. This improoves overall balance AND brings the output impedance to the 200 ohms stated by MXL.
Better: only replace R1 by 180 ohms. Then adjust R2 for best balance by means of a trimpot. See bottom of this page for how to measure.
3) Replace C14 and C15 by 0,47uF film condenser ( !! difference max 1% !!). This will lower the output impedances for frequencies below 200Hz, so induced hum will be weaker. Due to 1% tolerance, balancing can improove upto 40dB. (At my MXL990's this improoved 50Hz hum suppression dramatically).
4) The drain current of the FET in the MXL990 was not optimal for lowest noise, maximal undistorted output, and highest input impedance (could be of influence with respect to low frequency charactersitic of the mike). I did change to higher drain current, but this is less simple, as there must also be made changes into the positive feedline to the FET and the 40V oscillator for the mike capsule, in order to get there the same voltage as before the modification.
5) Idea: put a ferrite bead in both signal wires directly onto XLRpins 2 and 3. This keeps out VHF/UHF signals and prevents noises from cellphones and VHF portophones.

Testing and optimizing the balancing effect:
12. Connect the microphone to a mixer and phantom power.
13. Connect a mono test signal through two resistors 1kohm 0,1% tolerance, each to XLR pins 2 and 3. Test signal 1.5kHz sinus, 50 ohm source impedance, 10mV-100mVrms.
14. Adjust the trimmer resistor until the output of the mixer is minimal. Measure the value of it, and replace it by means of a fixed resistors 1% .
15. Then check the balancing effect at 50Hz by disconnecting and reconnecting the 1kohm resistor at pin3, and observing the difference in mixer output. Repeat at 5kHz and 50kHz. It should be better than 20dB.


For old type Behringer C2 mikes see my site.

Nico, pa0nhc.
Old 8th June 2010
  #25
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MXL internal connections

Just to quote this old thread, now three years on...
I have a MXL mic with the same circuit boards, and wondering where the lower of the two internal white wires goes between the two boards?
There are two white wires and one red wire. The lower of the two white ones has come loose - a previous owner's re-housing project gone wrong. I think it goes to ground/earth, but just checking as I'm not that great with electronics, but can figure out a thing or two..
It seems to come off the ground section of the diaphragm board, so I imagine it just connects back up to the pretty much any part of the earth pad on the second board.
I can post some images if that would help?
thanks!
Evan. (first post on Gearslutz!)
Old 9th June 2010
  #26
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During the time between that post and this one I breadboarded a mike with capsules from the same MXLs, this time with one dual triode 6N2P and a pair of P-type MOSFETs. I figured out how to go without noisy gigaohm resistors. Sound was impressive: very low noise, huge headroom limited by saturation of transformers only, but I postponed the project because of other projects. I will need an original, nice looking body for X-Y stereo mike.
Old 9th March 2014
  #27
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Quote:
Originally Posted by Wavebourn View Post
During the time between that post and this one I breadboarded a mike with capsules from the same MXLs, this time with one dual triode 6N2P and a pair of P-type MOSFETs. I figured out how to go without noisy gigaohm resistors. Sound was impressive: very low noise, huge headroom limited by saturation of transformers only, but I postponed the project because of other projects. I will need an original, nice looking body for X-Y stereo mike.

Got a schematic? I've got a V57M I wouldn't mind sacrificing to try that out.
Old 4th December 2016
  #28
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Quote:
Originally Posted by cjgrier View Post
Got a schematic? I've got a V57M I wouldn't mind sacrificing to try that out.
It is enough in V57 to replace 1 resistor that pulls base current by a 2-resistor voltage divider to make a decent microphone from it. The problem is, modern transistors have higher Beta than vintage German ones, and spread of Beta is wider. People who copied the design did not take this into an account, as the result distortions are higher, and all microphones distort on different SPL levels.
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